Process for dehydrogenation of alkylaromatic hydrocarbons using a dehydrogenation catalyst

ABSTRACT

A catalyst for the production of alkenylaromatics from alkylaromatics, wherein the catalyst is predominantly iron oxide, an alkali metal compound and a small amount of a source for palladium or platinum. Additional components of the catalyst may include compounds based on cerium, molybdenum, tungsten and other such promoters. Also a process for the production of alkenylaromatics from alkylaromatics using this catalyst.

This application is a divisional of application Ser. No. 09/053,234filed on Apr. 1, 1998.

BACKGROUND OF THE INVENTION

The field of art to which this invention pertains is dehydrogenationcatalysts.

In the catalytic dehydrogenation of alkylaromatic hydrocarbons toalkenylaromatic hydrocarbons, e.g., the dehydrogenation of ethylbenzeneto styrene, considerable efforts have been expended to develop catalystswhich exhibit high conversion combined with high selectivity andincreased stability.

Promoted iron oxide catalysts have been found to be especially useful inthe dehydrogenation of alkylaromatic hydrocarbons to alkenylaromatichydrocarbons. Typical commercial iron oxide-based dehydrogenationcatalysts are generally promoted with the addition of other metalcompounds, in the form of, but not limited to, oxides, hydroxides,carbonates, nitrates, etc. Often one of the promoters is an alkali metalcompound with potassium being preferred. Other components may also beadded to the dehydrogenation catalyst to provide further promotion,activation or stabilization. In all such dehydrogenation catalysts,minor amounts of modifiers are also typically present, such as organicburn-out agents: carbon black, graphite, methylcellulose, etc., whichcan beneficially effect the pore structure and/or other physicalproperties of the catalyst. In the discussion of the different metalgroups, the reference will be based on the new IUPAC notation of theperiodic table.

Typical catalysts used in dehydrogenation of saturated hydrocarbons tounsaturated hydrocarbons, as disclosed in U.S. Pat. No. 2,866,790, areiron oxide catalysts containing a small amount of chromium oxide as astabilizer and a small amount of potassium compound as promoter.Improved catalysts according to this patent are made from iron oxide (39to 47 weight percent), chromium oxide (1 to 10 weight percent), andpotassium carbonate (51 to 59 weight percent).

Dehydrogenation catalysts having good physical strength are described inU.S. Pat. No. 2,866,791. These catalysts are made from 51 to 59 weightpercent potassium fluoride, 1.0 to 10 weight percent chromium oxide withthe balance being iron oxide (39 to 47 weight percent).

Catalysts designed for the dehydrogenation of alkylbenzenes, at elevatedtemperatures in the presence of steam, comprising iron oxide and as apromoter from about 1 to about 25 percent by weight of an alkali metaloxide, from about 1 to about 10 percent by weight of a rare earth metaloxide, and from about 0.1 to about 10 percent by weight calcium oxide,are disclosed in U.S. Pat. No. 4,749,674.

Another catalyst for the dehydrogenation of ethylbenzene to styrenedisclosed in U.S. Pat. No. 5,510,552 contains at least one iron oxide,at least one bicarbonate, oxide or hydroxide of potassium and/or cesium,an oxide, carbonate, nitrate or hydroxide of cerium, a hydraulic cement,from about 0.2 to about 10 percent of a sodium oxide and from about 1.5to about 20 percent calcium oxide.

WO 96/18458 discloses a method of preparing an iron oxide catalystcomprising contacting an iron oxide with a additive comprising anelement selected from a large group of elements on the periodic chart,heating that iron oxide mixture to a temperature of at least about 600°,to afford structural rearrangement of the particle habit of said ironoxide, and then forming it into the catalyst. See also WO 96/18594 andWO 96/18593.

Similarly, U.S. Pat. No. 5,668,075 discloses the preparation of improvedselectivity iron oxide dehydrogenation catalysts based on reconstructediron oxides. The reconstruction of the oxides comprises contacting aniron oxide with a dopant substance comprising elements selected from alarge group of components of the periodic chart and heating the dopediron oxide to a temperature of at least about 600° C., preferably 800°C. and 1100° C. As in the previous references, rearrangement of particlehabit is induced in iron oxide prior to it being formed into catalyst.Metal additives, disclosed in the teachings of the patent, are solelyand specifically used to promote the physical transformation of the ironoxide and not the chemical properties of the catalyst formed based onthe oxide.

Another dehydrogenation catalyst, which contains smaller amounts of ironoxide and relatively larger amounts of cerium oxide and potassiumcarbonate, is disclosed in U.S. Pat. No. 4,758,543.

Catalysts having good activity and good selectivity are described inU.S. Pat. No. 3,904,552. These catalysts are made with iron oxide andalkali metal oxides plus molybdenum oxide and cerium oxide. Similarcatalysts utilizing tungsten oxide in place of molybdenum oxide aredescribed in U.S. Pat. No. 4,144,197.

Dehydrogenation catalysts which maintain high activity and selectivityover extended periods of time are described in U.S. Pat. No. 4,467,046.These catalysts contain iron oxide, an alkali metal compound, a ceriumcompound, a molybdenum compound and a calcium compound.

Improving stability of Fe/K/Ce/Mo/Ca/Mg oxide catalysts by incorporationof small amounts of chromium (100 to 5000 ppm) into the iron oxide priorto forming the catalyst is taught in U.S. Pat. No. 5,023,225.

The addition of titanium also results in improved activity andselectivity of iron oxide/potassium oxide catalytic systems, forethylbenzene to styrene dehydrogenation, according to U.S. Pat. No.5,190,906.

Dehydrogenation catalysts made from iron oxide, chromium oxide andkaolinite plus potassium oxide are disclosed in U.S. Pat. No. 4,134,858.The catalysts can also contain at least one oxide of copper, vanadium,zinc, magnesium, manganese, nickel, cobalt, bismuth, tin, or antimony.

U.S. Pat. Nos. 3,424,808 and 3,505,422 are directed to dehydrogenationcatalysts which consist essentially of iron oxide, a minor amount of analkali metal hydroxide or carbonate, and a minor amount of transitionmetal, preferably ruthenium, cobalt, or nickel.

Catalysts for the dehydrogenation of para-ethyltoluene topara-methylstyrene are described in U.S. Pat. Nos. 4,404,123; 4,433,186;4,496,662; and 4,628,137. These catalysts are made with iron oxide andpotassium carbonate, plus chromic oxide, gallium trioxide, or magnesiumoxide. Each patent also discloses that the catalysts can optionallycontain compounds of cobalt, cadmium, aluminum, nickel, cesium, and rareearth elements as stabilizers, activators and promoters. Otherdehydrogenation catalysts and procedures for their use and manufactureare shown in U.S. Pat. Nos. 2,408,140; 2,414,585; 3,360,579; 3,364,277;and 4,098,723.

Dehydrogenation reactions are normally conducted at the highestpractical throughput rates to obtain optimum yield. Yield is dependentupon conversion and selectivity of the catalyst.

Selectivity of the catalyst is defined as the proportion of the desiredproduct, e.g., styrene, produced to the total amount of feedstock, e.g.,ethylbenzene, converted. Activity or conversion is that portion of thefeedstock which is converted to the desired product and by-products.

Improvements in either selectivity or activity can result insubstantially improved operating efficiency. Higher activity catalysts,for example, would allow operation at lower temperatures than currentlyavailable catalysts, for any given conversion. Thus, in addition to highenergy efficiency, the catalyst would be expected to last longer andgenerate less thermal by-products.

The ratio of benzene to toluene, B/T ratio, in the final product isanother criteria to be used in determining effectiveness of thecatalyst. The benzene by-product produced can be recycled for laterprocessing. Toluene can not be easily recycled and is considered anundesirable by-product. Thus catalysts yielding higher B/T by-productratio, all other factors the same, will be preferred.

There is thus a need for a dehydrogenation catalyst which has goodselectivity and activity.

It is, therefore, an object of the invention to provide a noveldehydrogenation catalyst.

It is another object of the invention to provide an improveddehydrogenation catalyst having both high activity and selectivity.

It is another object of this invention to provide an improved catalystfor the conversion of ethylbenzene to styrene, with high activity andhigh selectivity.

It is another object of the invention to provide an improveddehydrogenation catalyst containing at least iron oxide, an alkali metaloxide, and palladium and/or platinum as a promoter.

It is still a further object of this invention to provide an improvedprocess for the production of olefinic compounds, particularly styrene.These and other objects are obtained by the product and process of thepresent invention.

SUMMARY OF THE INVENTION

This invention is directed to an improved dehydrogenation catalyst,preferably for use in the dehydrogenation of ethylbenzene to styrene.

The catalyst of this invention is comprised of about 30 to about 90weight percent of at least one iron compound, about 1 to about 50 weightpercent of a compound selected from the group consisting of oxide,hydroxides, carbonates and bicarbonates of alkali metals, and about 0.1ppm to about 5000 ppm of palladium and/or platinum, wherein said weightpercents are based on the total catalyst weight. Preferably, palladiumis used. In addition, preferably, the catalyst also contains one or moreof the compounds selected from cerium, molybdenum or tungsten, magnesiumor calcium, a Group 4 metal, preferably titanium, and chromium.

The invention is also directed to a process for the production ofolefinic compounds by dehydrogenation, utilizing the above-describedcatalyst. The invention is preferably an improved process for theproduction of styrene from ethylbenzene utilizing the above-describedcatalyst.

DESCRIPTION OF THE INVENTION

The catalysts of this invention are made by combining an iron compound,such as iron oxide or a ferrite, preferably potassium ferrite, with analkali metal source, which can be in the form of, but is not limited to,oxides, hydroxides, carbonates, nitrates or bicarbonates, preferably asodium or potassium derivative, and most preferably potassium carbonate,and a source for palladium or platinum, with palladium being preferred.The source for palladium and/or platinum may include elemental platinum,elemental palladium, compounds containing palladium and/or platinum orcombination thereof.

In addition to the above-described components, the catalyst preferablyalso includes as promoters an oxide or salt of the lanthanides havingatomic number of 57 to 62, most preferably cerium. The catalystpreferably also includes molybdenum or tungsten compounds, preferablyoxides, most preferably molybdenum oxide. The catalyst preferably alsoincludes alkaline earth metal compounds, most preferably magnesium oxideor calcium oxide. The catalyst may also include a source for titanium,chromium or silicon or aluminum, preferably an oxide or salt. Thecatalyst may also include a source for at least one of the followingelements including zinc, manganese, copper, cobalt and vanadium andcombinations thereof.

In a preferred embodiment, the catalyst of this invention is composed ofabout 30 to about 90 weight percent iron oxide calculated as Fe₂O₃,about 1 to about 50 weight percent of the oxide, hydroxide, carbonate,or bicarbonate of an alkali metal, calculated as an oxide and about 0.1ppm to about 5000 ppm of platinum and/or palladium, preferablypalladium, wherein said weight percents are based on the total catalystweight. Preferably, the catalyst also contains as promoters one or moreof the following: about 0.5 to about 25 weight percent cerium oxidecalculated as CeO₂, from about 0.5 to about 10.0 weight percentmolybdenum oxide or tungsten oxide calculated as MoO₃ or WO₃, from about0.2 to about 10.0 weight percent an alkaline earth metal oxide,preferably magnesium or calcium oxide. Additional components of thecatalyst may include from about 50 ppm to about 4.0 weight percent ofchromium oxide calculated as Cr₂O₃ and from about 10 ppm to about 2000ppm of titanium oxide calculated as TiO₂. The catalyst may also includefrom about 0.1 to about 10.0 weight percent of the salt or oxide of oneor more of the following: aluminum, silicon, zinc, manganese, cobalt,cadmium, vanadium and copper, alone or in combination, calculated on anelemental basis.

An effective dehydrogenation catalyst contains from about 40 to about 90weight percent iron oxide calculated as Fe₂O₃, from about 5 to about 20weight percent of an alkali metal compound calculated as an alkali metaloxide, from about 0.1 ppm to about 1,000 ppm of a source of palladium orplatinum selected from the group including elemental palladium,elemental platinum, compounds containing palladium, compounds containingplatinum and combinations thereof, from about 0.5 to about 10.0 weightpercent of a molybdenum or tungsten compounds calculated as MoO₃ or WO₃,and from about 4.0 to about 12.0 weight percent of a cerium compound,calculated as CeO₂, wherein all weight percents are based on the totalweight of the catalyst. Additional promoters may be included with thiscatalyst as discussed above.

A most preferable dehydrogenation catalyst contains from about 40 toabout 90 percent iron oxide calculated as Fe₂O₃, about 5 to about 20percent of an alkali metal compound, preferably potassium oxide, about4.0 to about 12 percent of cerium oxide calculated as CeO₂, about 0.5 toabout 10.0 percent of molybdenum or tungsten oxide calculated as MoO₃ orWO₃, preferably molybdenum oxide, about 0.2 to about 10.0 percent ofcalcium or magnesium oxide, preferably calcium oxide, about 10 ppm toabout 1000 ppm of titanium oxide calculated as TiO₂, about 100 ppm toabout 2000 ppm of chromium oxide calculated as Cr₂O₃, and about 1 ppm toabout 1000 ppm of a source for palladium or platinum, preferablypalladium, calculated on an elemental basis. Additional components thatcan be added to this catalyst include from about 0.1 to about 10.0weight percent of an oxide of aluminum, silicon, manganese, copper,zinc, cadmium, vanadium, and cobalt, calculated on an elemental basis.

It is advantageous to prepare the catalyst using one or a combination ofthe following methods: co-precipitation, decomposition, impregnation andmechanical mixing or any other method, as would be readily appreciatedby those skilled in the art. The method chosen should guarantee intimatemixing and uniform distribution of the components.

It is well established in the art that different forms of iron oxide,red, yellow, brown and black, can be used for preparation of thedehydrogenation catalyst. Likewise, it is known in the art that the ironoxides can be derived from a variety of precursor materials, bothnatural and synthetic, using a number of processes. Generally, iron isadded to the catalyst compositions as red iron oxide, Fe₂O₃, or yellowiron oxide, Fe₂O₃.H₂O, but others can be readily utilized as would beappreciated by those skilled in the art. Particularly suited are pigmentgrades of the iron oxides. Ferrites may also be used, such as potassiumferrite.

Likewise, the catalyst promoter can be any material taught by the art,for example, an alkali metal compound(s). Potassium compounds are thepreferred alkali metal promoters. The promoter can be added to thecatalyst in various forms. Alkali metal oxides, hydroxides, carbonates,bicarbonates, and the like, and mixtures thereof are preferred, withpotassium carbonate or a mixture of potassium carbonate with potassiumoxide is most preferred.

The catalyst compositions of the present invention also may contain, andpreferably do contain compounds of cerium to enhance conversion and/orselectivity depending on the co-promoters. Cerium, if used in thecatalyst compositions of the present invention, can be added to thecatalyst in the form of cerium oxide or in the form of other ceriumcompounds, as for example, cerium carbonate, cerium nitrate, ceriumhydroxide, or any combination thereof.

Other known catalyst additives can be included in the catalysts of thepresent invention, but are not essential. A chromium compound, which canserve as a stabilizer for the active catalytic components, isillustrative of an optional, but preferred, additive. Chromium compoundsare added to alkali-promoted iron oxide catalysts to extend their lifeand improve stability at low steam to oil conditions of operation.Chromium, as used in the compositions of the present invention, can beadded to the catalyst in the form of a chromium oxide or in the form ofa chromium salt. Preferably, chromium is added by spiking of the ironoxide used in catalyst preparation as taught in U.S. Pat. No. 5,023,225.

The addition of titanium is taught in U.S. Pat. No. 5,190,906. Otheroptional components, used to improve selectivity of the catalyst,include molybdenum or tungsten, which can be added as respective oxidesor salts, including derivatives of corresponding oxo acids (i.e.molybdates or tungstates, respectively). In addition, a number of othermetal compounds may be added as promoters. These can include, but arenot limited to, compounds of aluminum, vanadium, cobalt, cadmium,copper, calcium, magnesium, and manganese.

The physical strength, activity and selectivity of the catalystcompositions of the present invention can be improved by adding certainbinding agents. Binding agents can include, but are not limited to,hydraulic cements, calcium aluminate or Portland cement. These agentscan be added individually or in combination.

The density of the catalyst composition can be modified by the additionof various filler substances, for example, combustible materials such asgraphite and methyl cellulose. Such materials can be added to thecompositions during preparation, but are burned out after the catalystpellets have been formed during the calcining step. Porosity promotingaids can also facilitate extrusion of catalyst pellets.

The catalyst components can be mixed in various ways known to the art.One method comprises ballmilling together a mixture of desiredcompounds, adding a small amount of water, and extruding the compositeto produce small pellets, which are then dried and calcined. Anothermethod is mixing the components together with water, drying them to forma powder, and tableting and calcining the tablets. Another procedureinvolves mixing the components together with an excess of water,partially drying, and then subsequently extruding, drying, and calciningthe resulting pellets. The choice of the mixing method depends on thepreference of the skilled artisan.

A preferred method of preparing the catalyst is to blend the catalystingredients together in the presence of sufficient water to make a moistextrudable mixture. This mixture is then extruded to produce extrudatesof desired shape and size, typically cylindrical pellets having adiameter of about 3 mm. The extrudates are then calcined underconventional calcining conditions. Calcination temperatures can rangefrom about 500° C. to about 1200° C., preferably from about 600° C. toabout 1000° C. After calcination, the extrudates are ready for use ascatalysts.

Known methods can be used to form the catalyst mass. Preferred formingmethods are pelletizing, extruding and tableting, in which the use ofinorganic or organic auxiliaries as lubricants to improve plasticityduring extrusion is recommended. Forming can also be undertaken bothbefore and after calcination.

The efficacy of the palladium or platinum addition is independent of themethod of addition or the point in the manufacturing process at which itis incorporated. The following are some methods for delivery of thepalladium or platinum promoter. A number of alternative methods would beobvious to one skilled in the art.

The palladium or platinum additives can be directly added to the ironoxide and the mixture can be pre-fired at about 300° C. to about 500° C.prior to blending with the other components. Alternatively, thepalladium or platinum can be co-precipitated with iron oxide prior tothe iron oxide being blended. In yet another embodiment, the palladiumand platinum additives can be impregnated onto the surface of thefinished catalyst followed by drying and re-calcination at a temperatureadequate to drive-off water and decompose the impregnated salt. However,addition of the palladium or platinum metal additives in the form of anaqueous solution of appropriate salts, preferably nitrates, directly tothe catalyst blend, immediately prior to mulling and pelletizing, ispreferred.

Heat treatment or calcination can be conducted under static conditions,for example, in a tray furnace, or under dynamic conditions, such as ina rotary kiln. The temperatures and residence times are determined foreach individual type of catalyst. The catalysts preferably occur asmoldings, especially in the form of spheres, pellets, rings, tablets orextruded products, in which they are formed as solid or hollow objectsin order to achieve a high geometric surface with a simultaneously lowresistance to flow.

The BET surface area of the catalysts is typically about 0.5 to about 12m²/g, and preferably, about 1.5 to about 4 m²/g. The BET surface isdetermined by N₂ adsorption, as described in ASTM D3663-92.

The specific pore volume is determined according to the mercurypenetration method described in J. Van Brakel, et al., PowderTechnology, 29, p.1 (1981). In this method, mercury is pressed up to apressure of about 4000 bar into the catalyst moldings, during which thevolume reduction of the mercury is plotted as a function of pressure. Acurve is obtained from which the pore distribution can also bedetermined. According to this mercury penetration method, only thevolume and distribution of pores with a diameter of >3.6 nm can bedetermined. Generally, catalysts with larger pore volume and highermedian pore diameter are preferred as taught in U.S. Pat. No. 5,689,023.Typical pore volume of the catalysts of the present invention is in therange of ca. 0.10 to 0.45 cc/g.

One skilled in the art will readily appreciate that surface area, totalpore volume and pore volume distribution can be adjusted with propermanufacturing techniques to get optimum performance for any givencatalyst composition. This not withstanding, the promotional effect ofpalladium or platinum addition to the formulations will still beunmistakable.

The catalysts of the present invention are effective as dehydrogenationcatalysts and especially effective in promoting the dehydrogenation ofethylbenzene to produce styrene. Such dehydrogenation reactions aregenerally carried out at reaction temperatures from about 480° C. toabout 700° C., preferably about 535° C. to about 650° C. The use ofsubatmospheric, atmospheric, or superatmospheric pressures are suitablefor the reactions. However, based on equilibrium and selectivityconsiderations, it is preferred to operate at as low a pressure as isfeasible. Therefore, atmospheric or subatmospheric pressure ispreferred. Typically the dehydrogenation process using the catalysts ofthis invention is conducted as a continuous operation utilizing a fixedbed which may consist of a single stage or a series of stages of thesame or different catalysts in one or more reactors. Other types ofreactors and reactor configurations can be used for the dehydrogenationprocess.

In the dehydrogenation process using the catalyst of this invention,steam is added to the hydrocarbon feedstock to aid in the removal ofcarbonaceous residues from the catalyst and to furnish heat for thereaction. Steam to hydrocarbon molar ratios from about 3 to about 18 orhigher can be used. However, in order to conserve energy in theoperation of the process, steam to hydrocarbon molar ratios (S/O) of 12or lower are preferred.

The contact time of the reactant-containing gas with the catalyst isexpressed in terms of liquid-hourly-space velocity (LHSV) which isdefined as the volume of liquid hydrocarbon reactant per volume ofcatalyst per hour. The LHSV of the organic reactants can vary betweenabout 0.1 hour⁻¹ and about 5 hour⁻¹.

When used in the continuous process of dehydrogenating ethyl benzene tostyrene, the catalysts of this invention exhibit better performance,i.e. higher conversion, improved yield and higher B/T ratio, thansimilar catalysts which do not contain palladium or platinum.

EXAMPLES

The following examples describe the invention in more detail. Parts andpercentages are by weight unless otherwise designated. Iron oxide usedin all the following preparations is a commercial product that maycontain ppm levels of Ti and Cr and may also contain minor amounts ofother elements such as Si, Al, Mn, Mg, S, Cl, Zn, V, Cu, etc.

Comparative Example 1

Comparative dehydrogenation catalyst 1, with a composition of 11.2%potassium oxide (K₂O), 88.8% iron oxide (Fe₂O₃) was prepared as follows:

A mixture of the required amounts of potassium carbonate and unhydratediron oxide were dry blended with a small amount of organiclubricant/poreformer, mixed with water to form an extrudable paste andthen formed into cylindrical pellets of 3 mm diameter. The pellets weredried several hours and then calcined (at 600° C.).

Example 2

The catalyst of Example 2 was prepared according to the procedure ofComparative Example 1, except that a palladium nitrate solutionsufficient to produce a concentration of 0.072% Pd in the final catalystwas added to the water used to prepare the extrudable paste.

The catalysts of Comparative Example 1 and Example 2 were tested forethylbenzene dehydrogenation performance in an externally heated tubularreactor of 1″ internal diameter. A vaporized, preheated mixture of steamand ethylbenzene (with a molar ratio of about 12/1) was introduced tothe catalyst at controlled throughput and pressure (LHSV=1 andpressure=1 atm.) over a range of temperature from 540° C. to 570° C.Dehydrogenated product exiting the reactor was collected and analyzed todetermine conversion (% C) of ethylbenzene and selectivity (% S) tostyrene. Table I shows the effect on performance of the catalystprepared according to the invention.

TABLE I Comparative Catalyst Example 1 Example 2 Palladium — 0.072concentration wt. % Dehydrogenation Performance % C % S % C % S 570° C.46.86 94.62 50.10 94.27 540° C. 25.62 96.15 33.30 96.04

Comparative Example 3

The dehydrogenation catalyst of Comparative Example 3 having thefollowing nominal composition on oxide basis:

9.89% K₂O

9.97% CeO₂

2.53% MoO₃

77.61% Fe₂O₃

was prepared as follows:

A mixture of the required amounts of potassium carbonate, ceriumcarbonate, molybdenum oxide, and unhydrated iron oxide were dry blendedwith a small amount of organic lubricant/poreformer, mixed with water toform an extrudable paste, and then formed into cylindrical pellets of 3mm diameter. The pellets were dried several hours and then calcined at900° C.

Examples 4 and 5

The catalysts of Examples 4 and 5 were prepared according to theprocedure for the catalyst of Comparative Example 3 except thatpalladium nitrate solution, Example 4, or dinitrodiamine platinumsolution, Example 5, sufficient to produce a concentration of 200 ppmpalladium or 368 ppm platinum in the respective calcined catalysts, wasadded to the water used to prepare the extrudable paste for pelletizingthe catalysts.

The catalysts of Comparative Example 3 and Examples 4 and 5 weregranulated (to a size of 0.85 to 1.18 mm) and evaluated for ethylbenzenedehydrogenation performance in a differential type reactor (steam/oil=12molar, p=1 atm., catalyst weight/feed rate=14.7 times (g. cat.×hr.÷mol).Dehydrogenation performance data are shown in Table II along with theindicated concentration of Pd or Pt. As in Comparative Example 1,catalyst performance was determined by analysis of the dehydrogenatedproduct exiting the reactor.

TABLE II Comparative Example 3 Example 4 Example 5 Promoter none Pd PtPromoter — 0.0200 0.0368 Concentration wt. % D.P.* % C % S % C % S % C %S 600° C. 30.73 98.41 35.94 98.21 35.54 98.51 585° C. 21.60 98.77 28.5698.63 27.59 98.90 570° C. 14.23 98.96 21.94 98.89 21.41 99.13 555° C. 9.15 99.09 16.32 99.08 16.15 99.25 540° C.  5.54 99.13 11.72 99.2012.16 99.32 *Dehydrogenation Performance

Comparative Example 6

The dehydrogenation catalyst of Comparative Example 6 having thefollowing nominal composition, on oxide basis:

9.89% K₂O

9.97% CeO₂

2.53% WO₃

77.61% Fe₂O₃

was prepared as follows:

A mixture of the required amounts of potassium carbonate, ceriumcarbonate, tungsten oxide, and unhydrated iron oxide were dry blendedwith a small amount of organic lubricant/poreformer, mixed with water toform an extrudable paste, and then formed into cylindrical pellets of 3mm diameter. The pellets were dried several hours and then calcined at900° C.

Examples 7 and 8

The catalysts of Examples 7 and 8 were prepared according to theprocedure for the catalyst of Comparative Example 6 except thatpalladium nitrate solution, Example 7, or dinitrodiamine platinumsolution, Example 8, sufficient to produce a concentration of 200 ppmpalladium or 368 ppm platinum in the respective calcined catalysts, wasadded to the water used to prepare the extrudable paste for pelletizingthe catalysts.

The catalysts of Comparative Example 6 and Examples 7 and 8 weregranulated (to a size of 0.85 to 1.18 mm) and evaluated for ethylbenzenedehydrogenation performance in the manner described in Example 3.Dehydrogenation performance data are shown in Table III along with theindicated concentration of Pd or Pt.

TABLE III Comparative Example 6 Example 7 Example 8 Promoter none Pd PtPromoter — 0.0200 0.0368 Concentration wt. % D.P.* % C % S % C % S % C %S 600° C. 30.18 98.55 43.04 97.87 37.12 98.58 585° C. 21.10 98.89 34.6098.43 28.79 98.95 570° C. 14.39 99.05 27.06 98.82 22.16 99.15 555° C. 9.49 99.15 20.65 99.00 16.78 99.28 540° C.  5.91 99.19 14.99 99.1712.74 99.37 *Dehydrogenation Performance

Comparative Example 9

The dehydrogenation catalyst of Comparative Example 9 having thefollowing nominal composition, on oxide basis:

9.5% K₂O

2.2% MgO

5.0% CeO₂

2.5% MoO₃

2.0% CaO

78.8% Fe₂O₃

was prepared as follows:

A mixture of the required amounts of potassium carbonate, magnesiumcarbonate, cerium carbonate, molybdenum oxide, calcium hydroxide andunhydrated iron oxide were dry blended with a small amount of organiclubricant/poreformer, mixed with water to form an extrudable paste, andthen formed into cylindrical pellets of 3 mm diameter. The pellets weredried several hours and then calcined (at 600° C.).

Examples 10, 11, 12, 13

The catalysts of Examples 10, 11, 12 and 13 were prepared according tothe procedure for the catalyst of Comparative Example 9 except thatamounts of a palladium nitrate solution, sufficient to produce thetarget concentration of palladium in the calcined catalyst, were addedto the water used to prepare the extrudable paste for pelletizing.

The catalysts of Comparative Example 9 and Examples 10 through 13 weregranulated (to a size of 0.85 to 1.18 mm) and evaluated for ethylbenzenedehydrogenation performance in the manner described in Example 3.Dehydrogenation performance data are shown in Table IV along with theindicated concentration of Pd.

TABLE IV Comparative Example 9 Example 10 Example 11 Example 12 Example13 Palladium Concentration wt. % — 0.12 0.064 0.031 0.010 D.P.* % C % S% C % S % C % S % C % S % C % S 600° C. 34.8 98.4 44.5 98.0 43.1 97.840.8 97.9 47.7 97.3 585° C. 24.1 98.9 36.4 98.5 34.7 98.3 33.0 98.3 39.298.1 570° C. 16.2 99.1 28.6 98.7 26.6 98.4 25.7 98.5 30.9 98.6 555° C.10.3 99.1 21.4 98.9 19.4 98.5 19.0 98.8 23.5 98.9 540° C.  6.4 99.1 15.898.9 13.5 98.5 13.5 98.9 17.0 99.2 *Dehydrogenation Performance

Comparative Example 14

The dehydrogenation catalyst of Comparative Example 14 having thefollowing nominal composition, on oxide basis:

9.4% K₂O

2.2% MgO

9.9% CeO₂

2.5% MoO₃

1.9% CaO

74.1% Fe₂O₃

was prepared as follows:

A mixture of the required amounts of potassium carbonate, magnesiumcarbonate, cerium carbonate, molybdenum oxide, calcium hydroxide andunhydrated iron oxide was dry blended with a small amount of organiclubricant/poreformer. Water was mulled into the mixture to form anextrudable paste. The paste was formed into cylindrical pellets of 3 mmdiameter. The pellets were dried several hours and then calcined at ca.840° C.

Examples 15, 16, 17, 18

The catalysts of Examples 15 through 18 were prepared in the manner ofthe catalyst of Comparative Example 14 except that amounts of apalladium nitrate solution sufficient to produce the targetconcentrations of Pd, in the calcined catalyst, were added to the waterused to prepare the extrudable paste for pelletizing each examplecatalyst.

The catalysts of Comparative Example 14 and Examples 15 through 18 weretested for dehydrogenation performance in the manner described inExample 3 except that the range of temperature was 538-593° C.Dehydrogenation performance data are shown in Table V along with theindicated concentration of Pd. Δ% C is the absolute deviation in %ethylbenzene conversion of the invention example catalysts versus thatof the comparative example catalyst. Δ% S₆₀ is the absolute deviation instyrene selectivity at 60% ethylbenzene conversion of the inventionexample catalysts versus that of the comparative example catalyst.Benzene to toluene, B/T, is the weight ratio of benzene to toluene inthe products.

TABLE V Catalyst Com. Ex 14 Example 15 Example 16 Example 17 Example 18Pd con., wt. % — 0.0023 0.0050 0.020 0.064 D.P*. at Temp. ° C. Δ % C B/TΔ % C B/T Δ % C B/T Δ % C B/T Δ % C B/T 593 0 .29 2.0 .30 1.6 .30 0.9.30 2.5 .32 565 0 .34 4.4 .37 4.0 .36 3.9 .37 4.7 .40 538 0 .50 7.6 .556.8 .50 6.3 .56 6.5 .57 ΔS₆₀ 0 −0.2 0.1 −0.2 −0.2 *DehydrogenationPerformance

Comparative Example 19

The dehydrogenation catalyst of Comparative Example 19 having thefollowing nominal composition, on oxide basis:

9.5% K₂O

2.2% MgO

5.0% CeO₂

2.5% MoO₃

2.0% CaO

78.8% Fe₂O₃

was prepared as follows:

A mixture of the required amounts of potassium carbonate, magnesiumcarbonate, molybdenum oxide, calcium hydroxide and unhydrated iron oxidewere dry blended with a small amount of organic lubricant/poreformer.The required amount of an aqueous solution of cerium nitrate was mulledinto the dry mixture to form an extrudable paste. The paste was formedinto cylindrical pellets of 3 mm diameter. The pellets were driedseveral hours and then calcined (at 600° C.).

Examples 20 and 21

The catalysts of Examples 20 and 21 were prepared according to theprocedure for the catalyst of Comparative Example 19 except palladiumnitrate solution, Example 20, or dinitrodiamine platinum solution,Example 21, sufficient to produce a concentration of 640 ppm palladiumor 1170 ppm platinum in the respective calcined catalysts, was added tothe water used to prepare the extrudable paste for pelletizing thecatalysts.

The catalysts of Comparative Example 19 and Examples 20 and 21 weretested in the manner described in Comparative Example 1. Dehydrogenationperformance data are shown in Table VI along with the indicatedconcentration of Pd or Pt in the example catalysts.

TABLE VI Catalyst Com. Ex 1 Example 20 Example 21 Promoter none Pd PtPromoter — 0.064 0.117 Concentration, wt. % D.P*. at Temp. ° C. Δ % C Δ% C Δ % C 600 0 0.1 0.5 570 0 5.3 4.1 540 0 9.5 7.3 Δ % S₆₀ 0  0.14 0.0

Comparative Example 22

The dehydrogenation catalyst of comparative Example 22 having thefollowing nominal composition, on oxide basis:

9.2% K2O

2.1% MgO

9.7% CeO2

3.9% WO3

1.9% CaO

73.2% Fe2O3

was prepared as follows:

A mixture of the required amounts of potassium carbonate, magnesiumcarbonate, ammonium metatungstate, calcium hydroxide and unhydrated ironoxide were blended together with enough water to form an extrudablepaste. The paste was formed into cylindrical pellets of 3 mm diameter.The pellets were dried several hours and then calcined at about 840° C.

Example 23

The catalyst of Example 23 was prepared as follows. A portion of thecatalyst prepared as Comparative Example 22 was post impregnated withpalladium nitrate, to a level of 0.02% Pd, using standard incipientwetness techniques.

The catalysts of Comparative Example 22 and Example 23 were tested inthe manner described in Comparative Example 14. Dehydrogenationperformance data are shown in Table VII.

TABLE VII Catalyst Com. Ex 22 Example 23 Pd Concentration, wt. % — 0.02D.P*. at Temp. ° C. Δ % C B/T Δ % C B/T 593 0 .16 1.6 .23 565 0 .16 4.7.27 538 0 N/A 7.0 .42 Δ % S₆₀ 0 −0.05 *D.P. = DehydrogenationPerformance

Comparative Example 24

Comparative dehydrogenation catalyst having the following nominalcomposition, on oxide basis:

9.0% K2O

2.1% MgO

9.5% CeO2

2.4% MoO3

2.1% CaO

74.8% Fe2O3

was prepared as follows:

A mixture of the required amounts of potassium carbonate, magnesiumcarbonate, cerium carbonate, molybdenum oxide, calcium hydroxide andunhydrated iron oxide were dry blended with a small amount of organiclubricant/poreformer, mixed with water to form an extrudable paste andthen formed into “ribbed” extrusions with a diameter of 2.8 mm (asdescribed in U.S. Pat. No. 5,097,091). The pellets were dried severalhours and then calcined (at ˜840° C.).

Example 25

The catalyst of Example 25 was prepared as follows. A portion of thecatalyst prepared as Comparative Example 24 was post-impregnated withpalladium nitrate, to a level of 50 ppm Pd, using standard incipientwetness techniques.

The catalysts of Comparative Example 24 and Example 25 were tested inthe manner described in Comparative Example 14. Dehydrogenationperformance data are shown in Table VIII.

TABLE VIII Catalyst Com. Example 24 Example 25 Pd concentration wt. % —0.005 D.P.* at Temp. ° C. Δ % C B/T Δ % C B/T 593 0 0.26 2.5 0.31 565 00.31 4.5 0.36 538 0 0.40 8.7 0.50 ΔS60 0 −0.17 *D.P. = DehydrogenationPerformance

The catalysts of the present invention display improved activity, whencompared to its unpromoted counterparts, as evidenced by increasedconversion at otherwise identical conditions. The improved conversion isachieved at no substantial loss in selectivity. Moreover, theby-products formed with palladium or platinum promoted catalysts, ofthis application, have higher benzene to toluene, B/T, ratio thanby-products formed with the non-promoted catalysts, Examples 2, 13through 18, 20, 21, 23 and 25 vs. comparative Examples 1, 17, 19, 22 and24, respectively.

Higher activity of the promoted catalysts is evident across thetemperature range of the process, as demonstrated by the results ofdifferential tests, Examples 4 and 5, 7 and 8, and 10 through 13 versusComparative Examples 3, 6 and 9 respectively. By definition theconversions achieved in this type of testing are lower than typical forcommercial operation. The advantage of the differential, micro-reactortests is that it probes the catalyst performance in kinetic regime, freeof diffusion interference, thus providing better, fundamental, insightinto promoter effects. On the other hand, whole particle, integral,isothermal reactor tests, such as Examples 14 on, reflect better theexpected commercial operation of the catalyst. The isothermal testsindicate that the activity increase in promoted catalysts is highest atthe lower range of typical operating temperatures in the ethylbenzene tostyrene dehydrogenation, Examples 10 through 22. However, this isprobably due to diffusional limitations of 3.00 mm pellets and not tolack of promoter effect. Analogous results, of integral tests on smallersize, shorter diffusion path, 2.8 mm ribbed extrusions styrene catalystdemonstrate this point. Higher activity, as evidenced by increasedconversion, is observed for Pd-promoted 2.8 mm ribbed extrusions ascompared to unpromoted version of the catalyst, Example 25 andComparative Example 24, respectively. The effect is evident across thetemperature range, up to 621° C. Notwithstanding, increased lowtemperature conversion of Pd promoted 3.00 mm pellets is especiallybeneficial in an adiabatic system that by default has part of the bedoperating at the lower end of the process temperature spectrum. The lowtemperature operation, for any given set conversion, in addition, bringsabout extended catalyst life and reduces fouling in the process ascompared to the unpromoted catalyst. Advantages resulting from increasedconversion of only a few tenths of a percent, not to mention on theorder of several percentage points as demonstrated in this invention,are extremely significant in commercial process which may produce manymillions of pounds of product per day.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed, sincethese are to be regarded as illustrative rather than restrictive.Variations and changes may be made by those skilled in the art withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A process for dehydrogenating a hydrocarbon feedstream in a hydrocarbon reaction zone, wherein the components of thestream when present in the reaction zone consist essentially of analkylaromatic hydrocarbon and steam, wherein the process consistsessentially of passing the hydrocarbon feed stream over adehydrogenation catalyst consisting essentially of about 30 to about 90weight percent of an iron compound calculated as an Fe₂O₃, about 1 toabout 50 weight percent of an alkali metal source calculated as analkali metal oxide, about 0.1 ppm to about 5000 ppm of at least one of apalladium or platinum source selected from the group consisting ofelemental palladium, elemental platinum, compounds containing palladium,compounds containing platinum and combinations thereof, wherein allweight percents are based on the total weight of the catalyst.
 2. Aprocess for dehydrogenating a hydrocarbon feed stream in a hydrocarbonreaction zone, wherein the components of the stream when present in thereaction zone consist essentially of an alkylaromatic hydrocarbon andsteam, wherein the process consists essentially of passing thehydrocarbon feed stream over a dehydrogenation catalyst consistingessentially of from about 40 to about 90 weight percent iron oxidecalculated as Fe₂O₃, from about 5 to about 20 weight percent of analkali metal compound calculated as an alkali metal oxide, from about 1ppm to about 1000 ppm of a source of palladium or platinum selected fromthe group consisting of elemental palladium, elemental platinum,compounds containing palladium, compounds containing platinum andcombinations thereof, from about 0.5 to about 10.0 weight percent of amolybdenum or tungsten compound, calculated as MoO₃ or WO₃ and fromabout 4.0 to about 12.0 weight percent of a cerium compound, calculatedas CeO₂, wherein all weight percents are based on the total weight ofthe catalyst.
 3. A process for dehydrogenating a hydrocarbon feed streamin a hydrocarbon reaction zone, wherein the components of the streamwhen present in reaction zone consist essentially of an alkylaromatichydrocarbon and steam, wherein the process consists essentially ofpassing the hydrocarbon feed stream over a dehydrogenation catalystconsisting essentially of from about 40 to about 90 weight percent ironoxide calculated as Fe₂O₃, from about 5 to about 20 percent of apotassium compound calculated as potassium oxide, from about 1.0 ppm toabout 1000 ppm of a source for platinum or palladium selected from thegroup consisting of elemental platinum, elemental palladium, compoundscontaining platinum, compounds containing palladium and combinationsthereof, from about 0.5 to about 10.0 weight percent of a molybdenum ortungsten compound calculated as MoO₃ or WO₃, from about 4.0 to about12.0 weight percent of a cerium compound calculated as CeO₂, from about0.2 to about 10.0 weight percent of a calcium or magnesium compoundcalculated as an oxide, from about 100 ppm to about 2000 ppm of achromium compound calculated as Cr₂O₃, and from about 10 ppm to about1000 ppm of a source for titanium calculated as TiO₂, wherein all weightpercents are based on the total weight of the catalyst.
 4. A process fordehydrogenating a hydrocarbon feed stream in a hydrocarbon reactionzone, wherein the components of the stream when present in reaction zoneconsist essentially of an alkylaromatic hydrocarbon and steam, whereinthe process consists essentially of passing the steam/alkylaromatic feedstream over a dehydrogenation catalyst consisting essentially of fromabout 40 to about 90 weight percent iron oxide calculated as Fe₂O₃, fromabout 5 to about 20 weight percent of an alkali metal compoundcalculated as an alkali metal oxide, from about 1 ppm to about 1000 ppmof a source of palladium or platinum selected from the group consistingof elemental palladium, elemental platinum, compounds containingpalladium, compounds containing platinum and combinations thereof, andfrom about 0.5 to about 10.0 weight percent of a molybdenum or tungstencompound, calculated as MoO₃ or WO₃, wherein all weight percents arebased on the total weight of the catalyst.
 5. A process fordehydrogenating a feed stream in a hydrocarbon reaction zone, whereinthe components of the stream when present in reaction zone consistessentially of an alkylaromatic hydrocarbon and steam, wherein theprocess consists essentially of passing the steam/alkylaromatic feedstream over a dehydrogenation catalyst consisting essentially of fromabout 40 to about 90 weight percent iron oxide calculated as Fe₂O₃, fromabout 5 to about 20 percent of a potassium compound calculated aspotassium oxide, from about 1.0 ppm to about 1000 ppm of a source forplatinum or palladium selected from the group consisting of elementalplatinum, elemental palladium, compounds containing platinum, compoundscontaining palladium and combinations thereof, from about 0.5 to about10.0 weight percent of a molybdenum or tungsten compound calculated asMoO₃ or WO₃, from about 4.0 to about 12.0 weight percent of a ceriumcompound calculated as CeO₂, from about 0.2 to about 10.0 weight percentof a calcium or magnesium compound calculated as an oxide, and fromabout 10 ppm to about 1000 ppm of a source for titanium calculated asTiO₂, wherein all weight percents are based on the total weight of thecatalyst.
 6. A process for dehydrogenating a hydrocarbon feed stream ina hydrocarbon reaction zone, wherein the components of the stream whenpresent in reaction zone consist essentially of ethyl benzene and steam,wherein the process consists essentially of passing the steam/ethylbenzene feed stream over a dehydrogenation catalyst consistingessentially of about 30 to about 90 weight percent of an iron compoundcalculated as an Fe₂O₃, about 1 to about 50 weight percent of an alkalimetal source calculated as an alkali metal oxide, about 0.1 ppm to about5000 ppm of at least one of a palladium or platinum source selected fromthe group consisting of elemental palladium, elemental platinum,compounds containing palladium, compounds containing platinum andcombinations thereof, wherein all weight percents are based on the totalweight of the catalyst.
 7. A process for dehydrogenating a hydrocarbonfeed stream in a hydrocarbon reaction zone, wherein the components ofthe stream when present in reaction zone consist essentially of ethylbenzene and steam, wherein the process consists essentially of passingthe steam/ethyl benzene feed stream over a dehydrogenation catalystconsisting essentially of from about 40 to about 90 weight percent ironoxide calculated as Fe₂O₃, from about 5 to about 20 weight percent of analkali metal compound calculated as an alkali metal oxide, from about 1ppm to about 1000 ppm of a source of palladium or platinum selected fromthe group consisting of elemental palladium, elemental platinum,compounds containing palladium, compounds containing platinum andcombinations thereof, from about 0.5 to about 10.0 weight percent of amolybdenum or tungsten compound, calculated as MoO₃ or WO₃ and fromabout 4.0 to about 12.0 weight percent of a cerium compound, calculatedas CeO₂, wherein all weight percents are based on the total weight ofthe catalyst.
 8. A process for dehydrogenating a feed stream in ahydrocarbon reaction zone, wherein the components of the stream whenpresent in reaction zone consist essentially of ethyl benzene and steam,wherein the process consists essentially of passing the steam/ethylbenzene feed stream over a dehydrogenation catalyst consistingessentially of from about 40 to about 90 weight percent iron oxidecalculated as Fe₂O₃, from about 5 to about 20 percent of a potassiumcompound calculated as potassium oxide, from about 1.0 ppm to about 1000ppm of a source for platinum or palladium selected from the groupconsisting of elemental platinum, elemental palladium, compoundscontaining platinum, compounds containing palladium and combinationsthereof, from about 0.5 to about 10.0 weight percent of a molybdenum ortungsten compound calculated as MoO₃ or WO₃, from about 4.0 to about12.0 weight percent of a cerium compound calculated as CeO₂, from about0.2 to about 10.0 weight percent of a calcium or magnesium compoundcalculated as an oxide, from about 100 ppm to about 2000 ppm of achromium compound calculated as Cr₂O₃, and from about 10 ppm to about1000 ppm of a source for titanium calculated as TiO₂, wherein all weightpercents are based on the total weight of the catalyst.
 9. A process fordehydrogenating a hydrocarbon feed stream in a hydrocarbon reactionzone, wherein the components of the stream when present in the reactionzone consist essentially of one or more alkylaromatic hydrocarbons andsteam, wherein the process consists essentially of passing thehydrocarbon feed stream over a dehydrogenation catalyst consistingessentially of from about 30 to about 90 weight percent iron oxidecalculated as Fe₂O₃, from about 1 to about 50 weight percent of analkali metal compound calculated as an alkali metal oxide, from about0.1 ppm to about 5000 ppm of a source of palladium or platinum selectedfrom the group consisting of elemental palladium, elemental platinum,compounds containing palladium, compounds containing platinum andcombinations thereof, from about 0.5 to about 10.0 weight percent of amolybdenum or tungsten compound, calculated as MoO₃ or WO₃ from about4.0 to about 12.0 weight percent of a cerium compound, calculated asCeO₂, and from about 0.2 to about 10.0 weight percent of a calcium ormagnesium compound, wherein all weight percents are based on the totalweight of the catalyst.
 10. A process for dehydrogenating a hydrocarbonfeed stream in a hydrocarbon reaction zone, wherein the components ofthe stream when present in the reaction zone consist essentially of oneor more alkylaromatic hydrocarbons and steam, wherein the processconsists essentially of passing the hydrocarbon feed stream over adehydrogenation catalyst consisting essentially of from about 30 toabout 90 weight percent iron oxide calculated as Fe₂O₃, from about 1 toabout 50 weight percent of an alkali metal compound calculated as analkali metal oxide, from about 0.1 ppm to about 5000 ppm of a source ofpalladium or platinum selected from the group consisting of elementalpalladium, elemental platinum, compounds containing palladium, compoundscontaining platinum and combinations thereof, from about 0.5 to about10.0 weight percent of a molybdenum or tungsten compound, calculated asMoO₃ or WO₃ from about 4.0 to about 12.0 weight percent of a ceriumcompound, calculated as CeO₂, and from about 10 ppm to about 1000 ppm ofa source for titanium, calculated as TiO₂, wherein all weight percentsare based on the total weight of the catalyst.
 11. A process fordehydrogenating a hydrocarbon feed stream in a hydrocarbon reactionzone, wherein the components of the stream when present in the reactionzone consist essentially of one or more alkylaromatic hydrocarbons andsteam, wherein the process consists essentially of passing thehydrocarbon feed stream over a dehydrogenation catalyst consistingessentially of from about 30 to about 90 weight percent iron oxidecalculated as Fe₂O₃, from about 1 to about 50 weight percent of analkali metal compound calculated as an alkali metal oxide, from about0.1 ppm to about 5000 ppm of a source of palladium or platinum selectedfrom the group consisting of elemental palladium, elemental platinum,compounds containing palladium, compounds containing platinum andcombinations thereof, from about 0.5 to about 10.0 weight percent of amolybdenum or tungsten compound, calculated as MoO₃ or WO₃ from about4.0 to about 12.0 weight percent of a cerium compound, calculated asCeO₂, and from about 50 ppm to about 4.0 weight percent of a chromiumcompound, calculated as Cr₂O₃, wherein all weight percents are based onthe total weight of the catalyst.
 12. A process for dehydrogenating ahydrocarbon feed stream in a hydrocarbon reaction zone, wherein thecomponents of the stream when present in the reaction zone consistessentially of one or more alkylaromatic hydrocarbons and steam, whereinthe process consists essentially of passing the hydrocarbon feed streamover a dehydrogenation catalyst consisting essentially of from about 30to about 90 weight percent iron oxide calculated as Fe₂O₃, from about 1to about 50 weight percent of an alkali metal compound calculated as analkali metal oxide, from about 0.1 ppm to about 5000 ppm of a source ofpalladium or platinum selected from the group consisting of elementalpalladium, elemental platinum, compounds containing palladium, compoundscontaining platinum and combinations thereof, from about 0.5 to about10.0 weight percent of a molybdenum or tungsten compound, calculated asMoO₃ or WO₃ from about 4.0 to about 12.0 weight percent of a ceriumcompound, calculated as CeO₂, and from about 50 ppm to about 4.0 weightpercent of a chromium compound, calculated as Cr₂O₃ and from about 10ppm to about 2000 ppm of a source for titanium, calculated as TiO₂,wherein all weight percents are based on the total weight of thecatalyst.
 13. A process for dehydrogenating a hydrocarbon feed stream ina hydrocarbon reaction zone, wherein the components of the stream whenpresent in the reaction zone consist essentially of one or morealkylaromatic hydrocarbons and steam, wherein the process consistsessentially of passing the hydrocarbon feed stream over adehydrogenation catalyst consisting essentially of from about 30 toabout 90 weight percent iron oxide calculated as Fe₂O₃, from about 1 toabout 50 weight percent of an alkali metal compound calculated as analkali metal oxide, from about 0.1 ppm to about 5000 ppm of a source ofpalladium or platinum selected from the group consisting of elementalpalladium, elemental platinum, compounds containing palladium, compoundscontaining platinum and combinations thereof, from about 0.5 to about10.0 weight percent of a molybdenum or tungsten compound, calculated asMoO₃ or WO₃ from about 4.0 to about 12.0 weight percent of a ceriumcompound, calculated as CeO₂, from about 0.2 to about 10.0 weightpercent of a magnesium or calcium compound and from about 50 ppm toabout 4.0 weight percent of a chromium compound, calculated as Cr₂O₃,wherein all weight percents are based on the total weight of thecatalyst.